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Full text of "PEM-INST-001: Instructions for Plastic Encapsulated Microcircuit (PEM) Selection, Screening, and Qualification"

NASA/TP— 2003— XXXXXX 






PEM-INST-001: Instructions for Plastic Encapsulated Microcircuit (PEM) 
Selection, Screening, and Qualification 



Prepared by: 

Dr. Alexander Teverovsky and Dr. Kusum Sahu 

Reviewed by: 

Dr. Henning Leidecker 

Approved by: 
Darryl Lakins 



National Aeronautics and 
Space Administration 

Goddard Space Flight Center 

Greenbelt, Maryland 20771 



May 2003 



The NASA STI Program Office ... in Profile 



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Hanover, MD 21076-1320 



NASAH'P— 2003-XXXXXX 



j>wr 



PEM-INST-001: Instructions for Plastic Encapsulated Microcircuit (PEM) 
Selection, Screening, and Qualification 



Prepared by: 

Dr. Alexander Teverovsky and Dr. Kusum Sahu, Goddard Space Flight Center, Greenbelt, MD 

Reviewed by: 

Dr. Henning Leidecker, Goddard Space Flight Center, Greenbelt, MD 

Approved by: 

Darryl Lakins, Goddard Space Flight Center, Greenbelt, MD 



National Aeronautics and 
Space Administration 

Goddard Space Flight Center 

Greenbelt, Maryland 20771 



May 2003 



Prepared by: 

Dr. Alexander Teverovsky, Senior Component Failure Analyst, 
QSS( Quality Support Services), 
Parts, Packaging, and Assembly Technologies Office 
Goddard Space-PitgRrCeijtgr, Greenbelt, MD 




Dr. Kusum Sahu, Principal Parts Engineer, Code 562 
Parts, Packaging, and Assembly Technologies Office 
Goddard Space FlighK^eiiter, Greenbelt, MD 



Reviewed by: 

Dr. Henning Leidecker, Chief Engineer, Code 562 
Parts, Packaging, and Assembly Technologies Office 
Goddard Space Flight Center, Greenbeh, MD 

Approved by: 

Darryl Lakins, Head, Code 562 

Parts, Packaging, and Assembly Technologies Office 

Goddard Space Flight Center, Greenbelt, MD 



/(iW^ //■ ^a^4fi4J> 



Available from : 

NASA Center for AeroSpace Information National Technical Information Service 
7121 Standard Drive 5285 Port Royal Road 

Hanover, MD 21076-1320 Springfield, VA 22161 

Price Code: A17 Price Code: AID 



PEM-INST-001 

Contents 

Page 1 of 44 



TABLE OF CONTENTS 

SECTION PAGE 

Table of Contents 1 

List of Tables 2 

List of Figures 2 

Preface 3 

1. NASA/GSFC PEMs Policy 4 

2. Product Assurance System for PEMs 6 

2.1 Scope 6 

2.2 Product Assurance System (Screening, 

Qualification, and DP A) 6 

2.3 Additional Evaluations 7 

2.4 Requirements for PEMs by Project Risk Levels 8 

3. P..equirements for Screening 9 

4. Requirements for Qualification 16 

5. Destructive Physical Analysis (DP A) 20 

5.1 Purposes ofDPA for PEMs 20 

5.2 DPA Test Flow 20 

5.3 GSFC DPA Procedure 22 

5.3.1 External Visual Examination 22 

5.3.2 Radiography 22 

5.3.3 Acoustic Microscopy (C-SAM) 22 

5.3.4 Package Level Cross-Sectioning 24 

5.3.5 Internal Visual Inspection 26 

5.3.6 Bond Pull Test 27 

5.3.7 Glassivation Layer Integrity 28 

5.3.8 Assembly Examination Usmg Scanning Electron Microscope (SEM) 28 

5.3.9 Die Metallization Examination Using SEM 28 

6. Evaluation Analysis 30 

7. Derating Requirements 31 

8. Handling and Storage Requirements 32 

9. Information From Manufacturers 33 

10. Appendix A: Basis for GSFC Policy on the Use of PEMs 35 

11. Appendix B: Product Assurance Methodology 43 



LIST OF TABLES 



PEM-INST-001 

Contents 

Page 2 of 44 



TABLE 



Table 1 


Table 2 


Table 2A 


Table 3 


Table 4 


Table 5 



GSFC PEM Requirements 

GSFC Screening Requirements for PEMS 

Bum-in and Electrical Measurement Requirements for PEMs 

GSFC Qualification Requirements for PEMS 

Derating Requirements for PEMs 

Manufacturer Information 



PAGE 

8 

10 

13 

18 

31 

33 



FIGURE 



LIST OF FIGURES 



PAGE 



Figure 1 Product Assurance System for PEMs and Its Relationship 

With Reliability During the Part Lifespan 

Figure 2 A Typical Test Flow for Screening of PEMs 

Figure 3 A Typical Qualification Test Flow for PEMs 

Figure 4 A Typical DPA Test Flow for PEMs 

Figure 5 PEM Evaluation Process 

Figure 6 GSFC Product Assurance System for PEMs 



7 

9 

17 

21 

42 

44 



PEM-INST-001 

Preface 

Page 3 of 44 



PREFACE 



Potential users of plastic encapsulated microcircuits (PEMs) need to be reminded that unlike the miUtary 
system of producing robust high-reliability microcircuits that are designed to perform acceptably in a 
variety of harsh environments, PEMs are primarily designed for use in benign environments where 
equipment is easily accessed for repair or replacement. The methods of analysis applied to military 
products to demonstrate high reliability cannot always be applied to PEMs. This makes it difficult for 
users to characterize PEMs for two reasons: 

1 . Due to the major differences in design and construction, the standard test practices used to ensure 
that military devices are robust and have high reliability often cannot be applied to PEMs that have 
a smaller operating temperature range and are typically more frail and susceptible to moisture 
absorption. In contrast, high-reliability military microcircuits usually utilize large, robust, high- 
temperature packages that are hermetically sealed. 

2. Unlike the military high-reUability system, users of PEMs have little visibility into commercial 
manufacturers' proprietary design, materials, die traceability, and production processes and 
procedures. There is no central authority that monitors PEM commercial product for quality, and 
there are no controls in place that can be imposed across all commercial manufacturers to provide 
confidence to high-reliability users that a common acceptable level of quality exists for all PEMs 
manufacturers. Consequently, there is no guaranteed control over the type of reliability that is built 
into commercial product, and there is no guarantee that different lots from the same manufacturer 
are equally acceptable. And regarding application, there is no guarantee that commercial products 
intended for use in benign environments will provide acceptable performance and reliability in 
harsh space environments. 

The qualification and screening processes contained in this document are intended to detect 
poor-quality lots and screen out early random failures from use in space flight hardware. 
However, since it cannot be guaranteed that quality was designed and built into PEMs that 
are appropriate for space applications, users cannot screen in quality that may not exist. It 

must be understood that due to the variety of materials, processes, and technologies used to design 
and produce PEMs, this test process may not accelerate and detect all failure mechanisms. While 
the tests herein will increase user confidence that PEMs with otherwise unknown reliability can be 
used in space environments, such testing may not guarantee the same level of reliability offered 
by military microcircuits. PEMs should only be used where due to performance needs there 
are no alternatives in the military high-reliability market, and projects are willing to accept 
higher risk. 



PEM-INST-001 

Section 1. NASA GSFC PEMs Policy 

Page 4 of 44 



1. NASA/GSFC PEMS POLICY 



The use of plastic encapsulated microcircuits (PEMs) is permitted on NASA Goddard Space Flight Center 
(GSFC) space flight applications, provided each use is thoroughly evaluated for thermal, mechanical, and 
radiation implications of the specific application and found to meet mission requirements. PEMs shall be 
selected for their functional advantage and availability, not for cost savings; the steps necessary to ensure 
reliability usually negate any initial apparent cost advantage. A PEM shall not be substituted for a form, 
fit, and functional equivalent, high-reliability, hermetic device in space flight applications. 

Due to the rapid change in wafer-level designs typical of commercial parts and the unknown traceability 
between packaging lots and wafer lots, lot-specific testing is required for PEMs, unless specifically 
excepted by the Mission Assurance Requirements (MAR) for the project. Lot-specific qualification, 
screening, and radiation hardness assurance analysis and/or testing shall be consistent with the required 
reliability level as defined in the MAR. 

Developers proposing to use PEMs shall address the following items in their Performance Assurance 
Implementation Plan: source selection (manufacturers and distributors), storage conditions for all stages of 
use, packing, shipping and handling, electrostatic discharge (ESD), screening and qualification testing, 
derating, radiation hardness assurance, test house selection and control, and data collection and retention. 
Use of PEMs outside the manufacturer's rated temperature range requires written approval from GSFC. 
Specifically, PEMs must be: 

• Stored under temperature-controlled, clean conditions, protected from ESD and humidity. 

• Traceable to the branded manufacturer. 

• Procured from the manufacturer or their approved distributor. 

• Tested to verify compliance with the performance requirements of the application environment 
over the intended mission lifetime. 

• Tested using practices and facilities with demonstrated capabilities sufficient to handle and test the 
technologies involved. 

Testing in accordance with EEE-rNfST-002 shall be performed as necessary to qualify and screen the 
devices, in order to verify compliance with the application requirements and project risk level defined in 
the program MAR. Radiation evaluation shall address all threats appropriate for the technology, 
application, and environment, including Total Ionizing Dose (TID), Single Event Effects (SEE), and 
displacement damage. Existing radiation data can be used only with the review and approval of the 
project radiation specialist. 

PEMs with manufacture dates older than 3 years before the time of installation shall not be used without 
GSFC approval. Derating of PEMs must be addressed with consideration of specific material, device 
construction, device characteristics, and application requirements. 

Use of PEMs with pure tin-plated terminations requires special precautions to preclude failures caused by 
tin whiskers. GSFC approval of mitigation strategies is required. 



PEM-INST-001 

Section 1. NASA GSFC PEMs Policy 

Page 5 of 44 



Exceptions to testing required by EEE-INST-002 may be permitted by GSFC on a case-by-case basis, 
where it can be demonstrated that either existing lot-specific test data show acceptable results, or the use 
of high-risk PEMs represents low risk of fiinctional loss should the part fail. All rationale for such 
exceptions shall be documented. 

NASA will use part performance data collected in accordance with this policy to evaluate the policy's 
effectiveness and to develop recommendations for fiature improvements and streamlining. 



PEM-INST-001 

Section 2. PEMs Product 

Assurance System 

Page 6 of 44 

2.0 PRODUCT ASSURANCE SYSTEM FOR PEMS 

2.1 Scope 

This document establishes a system of product assurance for PEMs in order to invoke the GSFC PEM 
pohcy. It is based partly on existing qualification system for military and aerospace components, 
experience accumulated by the parts engineering community, and practices or guidelines established by 
high-reliability electronics industry. 

2.2 Product Assurance System (Screening, Qualification, and DP A) 

Purpose. The purpose of this product assurance system is to mitigate the risk of PEM usage, evaluate 
long-term reliability of the parts, and prevent failures. Commercial PEMs are primarily designed for 
benign environments and are considered as high-risk parts when used in space applications. For this 
reason, no PEMs are considered acceptable in high-reliability applications "as is" without 
additional testing and analysis to assure adequate reliability and radiation tolerance. 

Primary Elements of the Product Assurance System 

Screening. The purpose of screening is to detect and remove defective parts and reduce infant mortality 
failures. The screening process proactively evaluates the reliability of the lot. 

Qualification. The purpose of qualification testing is to ensure that no wear-out mechanisms would cause 
premature failures during the part storage, ground phase integration period, and spacecraft mission. The 
qualification process provides information regarding reliability of the design and the technology. 

Radiation Hardness . Radiation effects on the parts (Total Ionization Dose [TID] and Single Event Effects 
[SEE]) must be assessed on a lot-specific basis according to the project requirements. 

Destructive Physical Analysis (DP A). The purpose of DP A is to determine whether the lot has any 
design, material, workmanship, or process flaws that may not show up during screening and qualification 
tests and cause degradation or failures during the hardware integration period and spacecraft mission 
lifetime. When obvious gross defects are revealed during DP A, it is usually an indication that 
manufacturer's processes are out of control, and a replacement of the lot might be required. Therefore, it 
is recommended that DPA should be performed prior to screening and qualification of the lot. 
Anomalies revealed by DPA raise concerns regarding quality and reliability of the parts. These concerns 
may be fiirther addressed by tailoring screening and qualification procedures or by performing additional 
design evaluation and testing of the parts (refer to Section 6). 

A relationship between the major elements of the product assurance system (screening, qualification, and 
DPA) and reliability of the parts can be illustrated using a classic bathtub-shaped curve of the lifespan 
failure rate shown in Figure 1 . The three elements of the system discussed have been widely used for 
high-reliability parts and remain the major means to provide high-quality PEMs for space projects. 



PEM-INST-001 

Section 2. PEMs Product 

Assurance System 

Page 7 of 44 



X{t) 



Infant 
mortality 




useful life 




time 



Figure 1. Product Assurance System for PEMs and Its Relationship 
With ReHability During the Part Lifespan 

2.3 Additional Evaluations 

Additional evaluations might be necessary to further mitigate risks associated with the use of PEMs. 
These assessments shall include: 

Design Evaluation. Additional part- and application-specific evaluations performed beyond standard 
screening, qualification, or DPA may be necessary. Refer to Section 6, which describes capabilities of 
this element of the product assurance system. 

Manufacturer History. The manufacturer's history of ability to produce consistent reliability and quality 
should be reviewed (refer to Section 9). 

Distributor. Use of reputable distributors is essential to avoid procurement of counterfeit parts. Use of 
brokers is not recommended. Distributor compliance to PEMs handling and storage requirements should 
be assessed. 



Qualification by Flight History. For all PEMs, qualification by flight history or similarity is not 

acceptable. Commercial PEM manufacturers are known to produce the same part number with die 
sourced from different wafer lots having different die revisions. The same part number may also be made 
by multiple production plants, processed according to requirements that vary between wafer and assembly 



PEM-INST-001 

Section 2. PEMs Product 

Assurance System 

Page 8 of 44 

plants. However, the history of parts' appUcation is important and allows addressing specific problems of 
design and technology of the parts revealed previously. 

2.4 Requirements for PEMs by Project Risk Levels 

Requirements for use of PEMs in GSFC projects are shown in Table 1 for different project risk levels 
defined in EEE-INST-001 . 

Table 1. GSFC PEM Requirements 1/ 



Selection Priority 


Screening 
(See Section 3) 


Qualification 
(See Section 4) 


DPA 

(See Section 5) 


Level 1 


X 


X 


X 


Level 2 


X 


X 


X 


Level 3 


X 


X 


X 



Notes: 

1/ 



PEMs qualified according to this document are intended for operation within the manufacturer's data sheet 
limits. Any uprating and use of PEMs outside the manufacturer's specifled range, particularly the 
temperature limits, is not acceptable. 



PEM-INST-001 

Section 3. PEMs Screening 

Page 9 of 44 



3.0 REQUIREMENTS FOR SCREENING 



General . Screening is the only element of the product assurance system, which is applied to all flight parts 
by testing and inspecting every sample, and proactively affects reliability of the lot. Refer to Tables 2 and 
2a for screening requirements of PEMs for projects of different risk levels. 

Handling . There are numerous data indicating that improper handling and testing of the parts can 
introduce more defects than are screened out. Therefore, extreme caution should be taken during 
handling, storage, and testing to reduce the possibility of electrostatic discharge (ESD), electrical 
overstress (EOS), contamination, and mechanical damage to the parts. This demands scrupulous attention 
to the practice and requirements of handling and storage of the flight parts. Guidelines and requirements 
for handling and storage of PEMs are described in Section 8 of this document. A typical test flow for 
screening of PEMs is shown in Figure 3. 



























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Figure 2. A Typical Test Flow for Screening of PEMs 
(See Table 2 for details of GSFC screening requirements for PEMs.) 



PEM-INST-001 

Section 3. PEMs Screening 

Page 10 of 44 



Table 2. Screening Requirements for PEMs 1/ 






Screen 


Test Method and Conditions 


Level 1 


Level 2 


Level 3 


1 . External visual, and 
serialization 2/ 


Per paragraph 5.3.1. 


X 


X 


X 


2. Temperature cycling 


MIL-STD-883, Method 1010, 
Condition B (or to the manufacturer's 
storage temperature range, whichever 
is less). 

Temperature cycles, minimum. 


20 


20 


20 


3. Radiography 3/ 


Per paragraph 5.3.2. 


X 


X 


X 


4. C-SAM inspection 4/ 


Per paragraph 5.3.3. 


X 


X 


X 


5. Initial (pre-bum-in) 
electrical measurements 
(EM) 5/ 


Per device specification, at 25 °C 

At mm. and max. rated operational 
temperatures. 


X 
X 


X 
X 


X 


6. Engineering review (steps 
1 to 5) 6/ 










7. Static (steady-state) 
bum-in (BI) test at 125 °C 
or at max. operating 
temperature 11 


MIL-STD-883, Method 1015, 
condition A or B. 

Hours, minunum depending on the 
BI temperature. 


240 hrs. at 

125 °C 

445 hrs. at 

105 °C 

885 hrs. at 85 

"C 

1,560 hrs. at 

70 °C 


160 hrs. at 

125 "C 

300 hrs. at 

105 °C 

590 hrs. at 85 

°C 

1,040 hrs. at 

70 °C 


160 hrs. at 

125 "C 

300 hrs. at 

105 °C 

590 hrs. at 85 

°C 

1,040 hrs. at 

70 °C 


7a. Post static Bl electrical 
measurements at 25 °C 


Per device specification. Calculate 
Delta when applicable. 


X 


X 


X 


9. Dynamic bum-in test at 
125 °C or at max. operating 
temperature 7/ 


MIL-STD-883, Method 1015, Cond. 

D. 

Hours, minimum. 


Same as 
test step 7. 


Same as 
test step 7. 


Same as 
test step 7. 


10. Final parametric and 
functional tests 


Per device specification (at 25 °C, 
maximimi, and minimum rated 
operating temperatures). 


X 


X 


X 


1 1 .Calculate percent 

defective (steps 7 to 10) 
6/ 


Maxmium acceptable PDA. 


5% 


10% 


10% 


12. Extemal visual/packing 

2/ 


Per paragraph 5.3.1 and Section 8. 


X 


X 


X 



Notes on next page. 



PEM-INST-001 

Section 3. PEMs Screening 

Page 1 1 of 44 

Notes to Table 2. Screening Requirements for PEMs 

1/ General 

1.1/ Screening is performed on 1 00% of flight parts. 

1.2/ Historically, only parts with tight lot-specific controls imposed during manufacturing had been allowed 
for applications in level 1 projects. Such a control is impossible for PEMs, and the suggested screening 
procedures are not considered as a substitute for manufacturing control, but rather as risk mitigation 
measures. 

1 .3/ It is the responsibility of the project parts engineer to submit screening test results to Code 562 for 
logging into the Code 562 PEM database. 

2/ It is recommended to combine the incoming/outgoing visual inspections with the serialization and 

packaging to reduce handling and possible damage to the parts. Serialization should be performed in such a 
way to allow a top side C-SAM inspection. Flight parts should be handled and stored in a maimer to 
prevent mechanical and ESD damage, contamination, and moisture absorption (see Section 8). 

3/ To minimize handling, only a top view X-ray inspection is required. Focus to inspect for wire sweeping and 

obvious defects in the part. Depending on the results of the top view X-ray and/or part construction, a side 
view may be required. 

4/ Acoustic Microscopy (C-SAM) 

4. 1/ General. Acoustic microscopy is performed to screen out defects at critical die surface and lead tip 
wire-bond areas of the parts and screening, except for power devices, is performed only at the top 
side. 

4.2/ Coated Die. Top side of the internal portion of the leads is inspected in PEMs with polymer die 
coating. Inspection of the die area is not required, as the die coating has a low acoustic impedance 
that appears as a &lse delamination. 

4.3/ Power Devices. For power parts, the bottom side inspection of die attachment might be replaced with 
the thermal impedance measurements. 

4.4/ Rejection Criteria. 

• Any measurable amoimt of delamination between molding compound and the die surface. 

• Any delaminations on the leads at wire bond areas. 

• Delaminations extending more than 2/3 the length of internal part of the leads. 

5/ Electrical Measurements 

5.1/ Special Testing. In addition to parametric and functional measurements per data sheets, supplement and/or 

innovative testing techniques (e.g. IDDQ leakage currents, thermal impedance, output noise, etc.) can be used to 
select better quality parts from the lot (cherry pick) as flight candidates. These techniques should be certified 
and approved by Code 562. 

5.2/ Failure modes (parametric or catastrophic) should be recorded for each failed part. 

6/ Engineering Review 

6.1/ More than 10% C-SAM rejects might require additional evaluation of thermo-mechanical integrity of the lot or its 
replacement. 

6.2/ Most established PEMs manufacturers guarantees 3-sigma level process minimum, which means that less than 0.27% 
of the parts can be out of specification. Excessive fallouts diuing initial electrical measurements at room temperature 
might be due to a poor quality of the lot or effect of temperature cycling performed before electrical measurements, 
or it might be an indication of problems with the testing lab. When excessive rejects are experienced, the project PE 
decides whether a lot replacement or additional evaluation is needed based on observed failure modes and results of 
failure analysis. Excessive rejects during initial electrical measurements might be a legitimate cause for lot 
replacement. 



PEM-EMST-OOl 

Section 3. PEMs Screening 

Page 12 of 44 



Notes to Table 2 (Continued). Screening Requirements for PEMs 

7/ Burn-in (BI) 

7.1/ General. Bum-in is a complex, product-specific test and if possible siiould be conducted by the 
manufacturer of the part. If a user performs this test, special care should be taken not to exceed 
maxunum current, voltage, and die temperature limits. 

7.2/ Burn-in Temperature. The BI temperature is a "stress" temperature used to precipitate failure of 
defective parts and is typically much higher than the operational temperature of the part, where the 
characteristics are guaranteed to remam withm the data sheet limits. Most PEM manufacturers use 
temperatures in the range fi-om 125 °C to 150 °C to periodically perform BI to monitor quality of their 
product. However, if the parts engineer is unable to justiiy the suitability of bum-in at 125 °C, the 
bum-in ambient temperature shall be limited to the maximum operating temperature per the device 
specifications provided by the manufacturer. 

7.3/ Junction Temperature. The junction temperature during BI testing should not exceed the absolute 
maximum rated junction temperature for the part. 

7.4/ Molding Material Glass Transition Temperature. When the die temperature is close to or exceeds the 
glass transition temperature (Tg) of the molding compound (MC), electrical and mechanical properties 
of MC may change significantly and new degradation mechanisms may cause failures of the part. For 
most molding compounds, Tg values exceed 140 to 150 °C, which gives a necessary temperature 
margin for 125 °C BI. Reliability of the PEMs, which are manufactured with low-Tg molding 
compounds (Tg < 120 °C), is difficuh to assess, and such parts are not recommended for space 
projects without additional extensive analysis and testing. Glass transition temperature measurements 
are recommended prior to BI if usage of low-Tg molding compound for the lot is suspected. 

7.5/ Protection. In some parts the sensitivity of the input/output ESD protection circuits increases with 
temperature and these circuits can be tumed on easily, at lower and/or shorter voltage spikes, than at 
room temperature. For this reason, special care should be taken to prevent possible power line 
transients during bum-in testing. 

7.6/ Excessive proportion of functional BI failures, even when the total number of failures is within the 

PDA limits, might be an indication of serious lot reliability problems. In these cases additional testing 
and analysis of the parts might be required. 

7.7/ Steady-state bum-in is performed on all linear and mixed-signal devices (see Table 2A for details on 
bum-in conditions). The duration of steady-state bum-in can be reduced 50% if the parts are to be 
subjected to dynamic bum-in testing. 

7.8/ Dynamic bum-in is not required for parts operating under steady-state conditions, e.g. vohage 
references, temperature sensors, etc. 

7.9/ Only one type of BI test, either static or dynamic, is required for level 2 and 3 parts. 

7.10/ Under special circumstances, when it is technically and economically viable, and for components, 

which are difficuh to assess at the piece part level, altemative testing in lieu of static and/or dynamic 
BI testing (for example, board-level bum-in) may be permitted. It is the responsibility of the project 
PE to document and submit a rationale for the technical feasibility and equivalency of the altemative 
testing to the project and GSFC Code 562 for approval. Board-level bum-in shall not be routinely 
substituted for piece part bum-in as a convenience. 



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PEM-INST-001 

Section 4. Qualification Requirements 

Page 16 of 44 

4.0 REQUIREMENTS FOR QUALIFICATION 

Qualification of PEMs is perfonned to evaluate long-term reliability by accelerating 
potential degradation processes that might cause wear-out failures of the parts. The major 
areas of reliability concern for PEMs are: 

1 . Mechanical Failures due to mechanical stresses in the package (package level 
wear-out). 

2. Contamination Failures caused by moisture and contamination in the molding 
compound or at the die surface. 

3. Wear-Out Failures related to the degradation processes in the die (die level wear- 
out). 

4. Radiation Effects Failures caused by die susceptibility to degradation caused by 
gamma-irradiation and high-energy charged particles. 

Solder Reflow Simulation and Extended Temperature Cycling are intended to 
demonstrate susceptibility of the parts to thermal stresses. Surface mount technology 
(SMT) PEMs experience a high temperature shock during solder reflow processes. The 
reflow temperature exceeds maximum processing temperatures experienced by parts 
during the curing of molding compounds and the glass transition temperature of the 
plastic. This can cause significant mechanical stresses, resulting in observable or latent 
damage to the package and die. 

Highlv Accelerated Stress Testing (HAST) is used to detect moisture- and contamination- 
related susceptibility to failures. 

High Temperature Operational Life (HTOL) Testing is performed at high temperatures 
and maximum operation voltage and is intended to accelerate most of the die-related 
degradation processes. 

A typical test flow for qualification of plastic encapsulated microcircuits is shown in 
Figure 4. Table 3 presents details of the GSFC requirements for the qualification of 
PEMs for projects of different reliability levels. 



PEM-INST-001 

Section 4. Qualification Requirements 

Page 17 of 44 



Visuai hspection. 
serisAzation 



Radiation 
testing 



I 



C-SAM 
(22 parts for TC) 



JL 



Moisture soak 
(168hf/85°Cy60%RH> 



Reflow 
siiiHJlation 



Temperature Cycling 
-55''C--H25''C 



I 



Electrical tests at 
thtSB tenywatures 



I 



C-SAM 
exanwiaiion 



I 



FA orEva^iation 



Resistance to 
soldering 



" ^ ^^ 



Electricai tests 8^ 
three tenpersrtures 



sut>grot^1 



Life test 1 25 *C 



Electricd tests at 
three tenyerrtures 




QusMcalion 
report 






Data base 
iog^ 



sU>sroup2 



HAST: 130C/85%/ 
Sehrs 



I 



Electriciri tests at 
three temperatures 




Figure 3. A Typical Qualification Test Flow for PEMs 
(See Table 3 for GSFC qualification requirements for PEMs.) 



PEM-INST-001 

Section 4. Qualification Requirements 

Page 18 of 44 



Table 3. GSFC Qualification Requirements for PEMs 1/ 



Process 


Sub Test 


Test Methods & Conditions 


OTY (Failures) 


Level 1 


Level 2 


Level 3 


1. Visual 
inspection & 
serialization 2/ 




Section 5, paragraph 5.3.1 of 
562-PG-8700.2.?? 


32 


32 


17 


2. Radiation 
analysis 




TID and SEE 


3/ 


3/ 


3/ 


3. Baseline 
C-SAM 


(Parts in subgroup 1 
only) 


Section 5, paragraph 5.3.1 of 
562-PG-8700.2 .?? 


22 


22 


N/A 


5. Preconditioning 


Moisture soak 4/ 


JESD22 - Al 13-B, para. 3.1.5, 
condition A (168 hours, +85 
°C, 60% RH). 


32 


32 


17 


SMT devices 

Reflow simulation 
(with flux 

application, cleaning, 
and drying) 


JESD22-A1 13-B, Table 2 and 
paragraphs 3 . 1 .6 through 3.1.9. 
Peak solder reflow temperatiu-e 

+235 °C. 


32 


32 


17 




Through-hole 
devices 

Resistance to 
soldering temperature 


JESD22-B106-B. 


32 


32 


17 


4. Electrical 
measurements 


Per device 
specification 


Measure at 25 °C, min. & max. 
rated temperatures. 


32(0) 


32(0) 


17(0) 


6. Life testing 

Subgroup 1 


HTOL, 125 °C 5/, 6/ 


MIL-STD-883, Method 1005, 
Cond. D 

Hours, minimum. 


22 
1,500 


22 
1,000 


10 
500 


Electrical 
measurement (per 
specification) 


Measure at 25 °C, min. & max. 
rated temperatures. 


22(0) 


22(0) 


10(0) 


6a. Temperature 
cycling 

Subgroup 1 


Temperature cycling 

51,11 


MIL-STD-883 Method 1010, 

Cond. B 

(-55 °C to +125 °C), cycles, 

minimum. 


22 
500 


22 
200 


10 
100 


Electrical 
measurement (per 
specification) 


Measure at 25 °C, min. & max. 
rated temperatures. 


22(0) 


22(0) 


10(0) 


C-SAM 8/ 


Section 5, paragraph 5.3.3. 


22 


22 


N/A 


DPA or FA 


9/ 


X 


X 


N/A 


7. Highly 
accelerated stress 
test (HAST) 

Subgroup 2 


Biased HAST 5/ 


JESD22-A1 10, with continuous 

bias 

(96 hours, +130 °C, 85% RH). 


10 


N/A 


N/A 


Unbiased HAST 5/ 


JESD22-A1 18, Condition A 
(96 hours, +130 °C, 85% RH). 


N/A 


10 


7 



Notes on next page. 



PEM-INST-001 

Section 4. Qualification Requirements 

Page 19 of 44 

Notes to Table 3. GSFC Qualification Requirements for PEMs 
1.1/ All parts shall be selected fi-om a screened lot. 

1 .21 It is the responsibility of the project parts engineer to submit qualification test results to Code 562 
for logging into the Code 562 PEM database. 

2.1/ This step is not performed if results of the screening are available. 

3/ Radiation hardness of the parts must be assessed on a lot-specific basis according to the project 

requirements. So that analysis can be completed prior to screening and qualification, unscreened 
samples can be used for this test. An additional nimiber of samples, depending on radiation 
requirements, shall be provided by the project to perform this test. 

4/ Moisture soak is performed as a part of preconditioning to mimic worst-case moisture absorption 

conditions of the PEM molding material, which could cause PEMs to be damaged during soldering 
to boards. 

5/ Conditions of the temperature cycling, HAST, and high temperature life testing (HTOL) can be 

tailored according to specifics of the device application per Code 562 approval. Guidelines for 
application-tailored qualification testing of PEMs shall be developed by Code 562. 

6/ The jimction temperature should not exceed the absolute maximum rated junction temperature for 

the part. If 125 °C ambient causes the maximum rated junction temperature to be exceeded, the 
ambient temperature should be decreased appropriately. 

II Temperature cycling is performed after HTOL testing on the same samples only for economic 

reasons. This test can be also performed on a separate group of parts if additional samples are 
provided (22, 22, and 10 samples for levels 1, 2, and 3, respectively). 

8/ This C-SAM examination is performed to estimate mechanical damage to the part due to 

temperature cycling and reflow simulation (or resistance to soldering test) by comparing acoustic 
images with the baseline measurement results. 

9/ Failure analysis is performed on any failures during qualification tests to determine whether they 

are caused by lot-related defects, manufacturing process problems, or improper testing. If no 
failures are observed, a special evaliiation (DP A) should be performed to ensure that no 
degradation of wire bonding, cratering, and mechanical damage to glassivation and metalliaation 
systems occurred (for level 1 and 2 parts only). 



Applicable Standards for Test Methods 

JESD22-A1 I3-B: Preconditioning of Nonhermetic Surface Mount Devices Prior to Reliability 

Testing. 
JESD22-B106-B: Resistance to Soldering Temperature for Through-Hole Mounted Devices. 
JESD22-A1 10-B: Highly Accelerated Temperature and Humidity Stress Test (HAST). 
JESD22-A1 1 8: Accelerated Moisture Resistance - Unbiased HAST. 



PEM-INST-001 

Section 5. DP A 

Page 20 of 44 

5.0 DESTRUCTIVE PHYSICAL ANALYSIS (DPA) 

This section describes purpose, test flow, and procedures for Destructive physical 
analysis (DPA) of commercial PEMs and is intended to supplement GSFC-S-31 l-M-70 
(Specification for Destructive Physical Analysis). 

5.1 Purposes of DPA for PEMs 

DPA, or Construction analysis (CA), provides important information regarding design, 
workmanship, and process defects related to a PEM manufacturer lot. This information 
can be used for tailoring of screening and qualification test plans to focus on specific 
areas of reliability concerns. 

DPA for PEMs should focus on three major areas of concern: integrity of the package, 
quality of assembly, and defects in the die. This analysis should also evaluate package- 
and die-level homogeneity of the lot. For this purpose, samples for DPA should be 
selected randomly from different portions of the lot. 

An important benefit of DPA is to provide for comparison analysis of design and 
technology, to identify product change, to provide baseline data in the event of 
subsequent failures and application problems, and to provide data for physics of failure 
analysis. 

5.2 DPA Test Flow 

A typical test flow for destructive physical analysis of PEMs is shown in Figure 5. 



PEM-INST-001 

Section 5. DPA 

Page 21 of 44 



















External visual 
examination 






i 






Radiography 






i 




Acoustic microscopy 
(C-SAM) 








"^ 


■"-« 


■^^ 


^^^ 






Paclrage cross section 
2 samples minimum 




Decapsulidion 
3 samples minimum 






\ 


t 






i 






Optical examination o 
cross section 


f 


Optical intemal 
examination 






i 




1 r 








SEM exam, of wire bond & 
glasslvation (as needecQ 






SEM examination of 
cross section 






i 






1 


' c 








p 


Wire bond pull test 




i 


DPA report 


i 






Glassivation integrity 
test 




1 


' 


\v 


Data base 
log-in 1- 


\k 1 


r 




J \ 


SEM examination 
(die metallization) 



















Figure 4. A Typical DPA Test Flow for PEMs 
(See Section 5.3 for GSFC DPA procedure.) 



Notes: 

1/ Requirements for die-level examinations in PEMs are the same as the requirements for hermetic 
military- or space-graded parts. 

2/ It is the responsibility of the parts lab or project engineer (when DPA is performed by a GSFC 
contractor) to submit a DPA report to Code 562 for logging into the PEM database. 



PEM-INST-001 

Section 5. DPA 

Page 22 of 44 

5.3 GSFC DPA Procedure 

5.3.1 External Visual Examination 

Inspect each sample (five samples minimum) at 3X to lOX magnification. One 
photograph of one typical device showing all markings shall be taken. All anomalies 
shall be photo-documented. Failure criteria of MIL-STD-883E, Method 2009, "External 
visual" shall be used as applicable. In addition, inspect for any evidence of lot 
dissimilarity and the following defects: 

Package deformation (nonplanarity, warping, or bowing). 

Foreign inclusions in the package, voids and cracks in the plastic encapsulant. 

Deformed leads; peeling, blistering, or corrosion of finishing. 

Condition of external leads and plating. 

Legibility and correctness of marking. 

Evaluate homogeneity of the lot (package level). 

5.3.2 Radiography 

The purpose of this examination is to detect internal defects of the package and to 
determine die and wire placement for fiiture decapsulation. Inspect all submitted samples 
for the following defects: 

• Foreign objects and voids in the encapsulant. 

• Voids in the die attach material. 

• Misaligned leads. 

• Burrs on lead frame (inside the package). 

• Poor wire bond geometry (wires that deviate fi-om a straight line from bond to 
external lead or have no arc from die bonding pad to lead). 

• Swept or broken wires. 

• Improper die placement. 

Radiographs shall be taken of each device in two views 90 degrees apart (top and side 
views). MIL-STD-883E, Method 2012, "Radiography" is applicable. 

Note: When real-time radiography is used for screening, the dose rate that the equipment 
emits should be estimated. Certain types of radiography can expose microcircuits to 
unusually high dose rates, such that damage can be introduced to sensitive parts. The 
Radiation Effects Group should be consulted as necessary. 

5.3.3 Acoustic Microscopy (C-SAM) 

All samples shall be subjected to acoustic micro-imaging analysis. The purpose of this 
examination is to nondestructively detect the following defects: 



PEM-INST-001 

Section 5. DPA 

Page 23 of 44 

• Delamination of the molding compound from the lead frame, die, or paddle (top 
side and bottom side separately). 

• Voids and cracks in molding compoimd. 

• Unbonded regions and voids in the die-attach material (if possible). 

5.3.3.1 C-SAM Requirements . The C-SAM procedure for screening should comply with 
the following requirements: 

• A clean bath and deionized water should be used during acoustic examinations of 
the flight parts. 

• The test personnel shall be ESD certified to NASA-STD-8739.7 "ESD control." 

• Depending on storage conditions of the parts, a 1-hour bake at 125 °C should be 
performed to remove moisture from the parts after immersion into the water bath 
of an acoustic microscope. 

5.3.3.2 Package Examination Sites. Examination of the package for voids, cracks, and 
delaminations shall be performed on each sample at six areas: 

1 . Interface between the die surface and molding compound (top view). 

2. hiterface between the lead fi-ame and molding compoimd (top view). 

3. hiterface between the die paddle periphery and molding compound (top view). 

4. Die-to-paddle attachment interface (if possible). 

5. Interface between the die paddle and molding compound (back view). 

6. Interface between the lead frame and molding compound (back view). 



Notes 



Combined C-mode scans can be performed to investigate more than one area 

during one scaiming run. 

A-scan data (wave form analysis) should be performed to verify any 

delaminations (if observed). 

Die-attach mspection shall be performed per MIL-STD 883E, Method 2030, 

"Ultrasonic inspection of die attach" for the parts with the die mounted onto a 

substrate or heat sink. This standard can also be applicable for other package 

types provided the resolution is adequate to detect voids in the attachment 

material. 

Package surface roughness, mold marks, stamped marking, and surface defects 

create additional ultrasonic wave reflections that hinder analysis results. Labels 

should be removed from the area to be scanned. 

Anomalies and/or delaminations (if observed) should be verified using A-scan 

analysis. 



PEM-rNST-001 

Section 5. DPA 

Page 24 of 44 

5.3.3.3 Evaluation Criteria. The following shall be considered gross defects and the lot 
shall be rejected: 

1 . Cracks in plastic package intersecting bond wires. 

2. Internal cracks extending from any lead finger to any other internal feature (lead 
finger, chip, die attach paddle) if the crack length is more than 0.5 of the 
corresponding distance. 

3. Any cracks in the package extending to the surface. 

4. Any void in molding compound crossing wire bond. 

5 . Any measurable amount of delamination between molding compound and die 
surface or lead frame in the area of wire bond (bonds to lead fingers or to the die 
paddle). 

Note : If rejectable internal cracks or delaminations are suspected, a polished cross section 
may be required to verify the suspected site. 

The following aspects shall be considered as reliability concerns and additional testing 
and screening of the lot might be necessary: 

1 . Delamination of more than half of the backside or top peripheral area of the 
interface between the paddle and molding compound. 

2. Delamination of the top tie bar or lead area of more than 0.5 of its length. 

3 . Delamination at the top of the die paddle of more than 0.5 of the periphery area. 

5.3.4 Package Level Cross-Sectioning 

Two devices, or 40% of the DPA samples, whichever is larger, shall be subjected to this 
examination. The purposes of this examination is to evaluate: 

Wire bonding (both to the die and lead frame). 

Die attachment for voiding and delamination. 

Integrity of molding compound/lead frame interface. 

Lead frame plating and external lead finish. 

Lead frame/molding compound interface to ensure that there is no direct path 

(along the leads) for moisture and contamination to reach the die. 

Inspect the following areas of the package and die for defects: 

Defects and cracks in the package. 

Condition of die attachment. 

Lead frame/molding compound delamination. 

Condition of wire bonding at contact pads. 

Contact pad cratering. 

Condition of wire bonding at lead frame. 



PEM-INST-001 

Section 5. DPA 

Page 25 of 44 

• Anomalies in molding compound (e.g., red particles might indicate the presence 
of red phosphorus used as a flame retardant; this type of flame retardant might 
cause part failure). 

SEM examination and X-ray microanalysis at the package level cross section is 
performed optionally or to get more details of anomalies observed during optical 
examination. This examination shall be focused on the following areas: 

• Lead finish materials. 

• Intermetallic formation at wire bond/contact pad interface. 

• Composition and structure of molding compound, lead fi-ame, and lead frame 
plating and finishing. 

• Assembly/molding compound integrity. 

5.3.4.1 Cross-Sectioning Procedure. Halfof the samples shall be sectioned along the 
leads of one side of the package and half along the leads of the other side of the package. 
The planes shall cross the package in a mutually perpendicular fashion along the leads in 
the vicinity of the paddle edge, approximately in the middle of the die. Parts with the 
paddle tie bars shall be sectioned along the bars. For samples, different planes shall be 
selected that cross different wire bonds to the die and to the leads. If suitable, a sample 
can be divided in two parts before potting. Each plane of cross section shall be examined 
microscopically first at a low power (30X to 60X) magnification and then at a high power 
magnification (75X to 200X). Optical examination of the bonds inspection shall be 
performed at up to XI, 000 magnification. Pictures of all defective bonds and package 
faults, as well as at least one picture of a typical bond, die attachment, and overall 
package layout, should be taken. 

5.3.4.2 Evaluation Criteria. The following defects shall be considered as gross defects 
causing the lot to be rejected: 

1 . Package cracks and delaminations: Any evidence of external cracks other than 
between the lead and plastic at the lead entrance; large voids and delamination at 
the die attachment, die surface, and lead finger tips. 

2. Bonding: Lifted and shifted bonds, excessive intermetallic formation at the 
periphery of the ball bond. 

3. Molding compound: Voids and cracks in vicinity of bonding wires, presence of 
red phosphorus or other corrosive materials. 

4. Leads: Pure tin (Sn) finishing of the leads, delamination of finishing. 

The following aspects shall be considered as reliability concerns and additional testing 
and screening of the lot might be necessary: 

1 . Package cracks and delaminations: Any evidence of delamination or cracking of 
more than 0.5 of the lead or tie bar length. 



PEM-lMST-001 

Section 5. DPA 

Page 26 of 44 

2. Bonding: Abnormalities in intermetallic compound formation, cratering. 

3. Die attach: Voidingof more than 50%. 

4. Molding compound: Foreign intrusions. 

5.3.5 Internal Visual Inspection 

Three samples minimum shall be subjected to this examination. 

5.3.5.1 Decapsulation Techniques. Descriptionof different decapsulation techniques 
including Milling, Manual Wet Etching, Chemical Jet Etching, or Plasma Etching can be 
viewed at (http://nepp.nasa.gov/DocUploads/E449EBC9-30F5-4400- 
9F4CD447CF85ED7E/61206 DPA%20for%20PEMs.pdf ). 

5.3.5.2 Verification of the Decapsulation Quality 

1 . Confirm acceptance of the specimen for fiarther bonding examination. At least 
25% or three wire bonds, whichever is more, should meet the following criteria: 
be clean, have no damage, and be exposed more than approximately two-thirds of 
their length. 

2. Confirm acceptance of the specimen for fiirther glassivation integrity and SEM 
examinations. At least 75% of the die area should be clean and have no damage 
caused by deprocessing. 

3. Record any defects induced by the decapsulation that might affect the DPA resuhs. 

5.3.5.3 Examination. The decapsulated device shall be examined microscopically, first 
at low-power magnification (30X to 60X) and then at high-power magnification (75X to 
200X) to determine the existence of the die-level and assembly-level defects and to verify 
the die lot homogeneity and quality of decapsulation. 

Pictures of all defects, as well as an overall internal view of the die and die marking, 
should be presented in the report. 

The purpose of this inspection is to evaluate the mechanical condition of die, condition of 
wire bonds, and condition of glassivation. 

When necessary to get more details on observed anomalies, SEM examination of wire 
bond and glassivation is performed to inspect for anomalies with intermetallic growth at 
wire bonds, and damage to glassivation. 

5.3.5.4. Evaluation Criteria . Evaluation criteria per MIL-STD-883E, Method 2013, 
"Internal visual inspection for DPA" are applicable. No device shall be acceptable that 
exhibits the following defects: 



PEM-INST-001 

Section 5. DPA 

Page 27 of 44 

• Glassivation pinholes, peeling or cracks (in particular those specific to filler 
particle-induced damage). 

• Metallization voids, corrosion, peeling, or lifting. 

• Wire bonds lifting, misplacement, and excessive deformation. 

• Additionally, die-level lot homogeneity shall be evaluated. 

5.3.6 Bond Pull Test 

Two devices or 40% of the DPA samples, whichever is larger, shall be subjected to this 
examination. Each sample which met the requirements per 4.3.5.2 shall be subjected to a 
destructive bond pull test. 

The purpose of this test is to evaluate bond strength, contact pad metallization adherence, 
and cratering. 

The wire bonds shall be pulled to destruction according to MIL-STD-883, Method 201 1, 
"Bond strength (destructive bond pull test)," Condition D. 

Note: According to MIL-STD-883, Method 201 1, the pull is applied by inserting a hook 
under the wire approximately in the center of the loop. Normally, decapsulation exposes 
approximately 75% of the loop (exposure of the wire-to-lead bond would weaken the 
bond strength due to chemical attack). The wire tension in which the pull force is not 
applied in the middle of the loop and part of the loop is buried in plastic may differ by a 
factor of two from the values identified in MIL-STD-883. This means that the rejection 
criteria per MIL-STD-883, Method 201 1, may not be applicable. 

Typically, the ball neck is the weakest site of a wire bond because it has been aimealed 
during ball formation. If another site of the wire bond is found to be broken, the site 
could indicate a problem (especially in the case of a ball lift). 

A wire bond strength test may be greatly influenced by the history of the sample. 
Thermocycling or storage of the sample under high temperature and hvimidity 
envirormients can cause deterioration of the wire bond strength. Enhanced degradation of 
the intermetallic region of the gold-aluminum wire bonding pad interface occurs in the 
presence of some flame retardants in epoxy molding compounds (such as those 
containing bromine or antimony). In some cases, to ensure an adequate quality of the part 
and its long-term reliability, different types of accelerated tests are recommended before 
the sample is subjected to the wire pull test. 

Results of the bond pull test shall be recorded in the DPA records. 



PEM-INST-001 

Section 5. DPA 

Page 28 of 44 



5.3.7 Glassivation Layer Integrity 



One sample or 20% of the lot, whichever is larger, which meets the requirements per 
5.3.5.2 shall be subjected to a glassivation layer integrity test. This test is performed to 
evaluate cracks, voids, and pinholes in glassivation. This examination shall be performed 
per MIL-STD-883E, Method 2021, "Glassivation layer integrity." 

5.3.8 Assembly Examination Using Scanning Electron Microscope (SEM) 

The purpose of this examination is to verify quality of wire bonding and glassivation 
integrity. It is performed if optical inspection reveals anomalies that require further 
analysis. Pictures of worst-case defective bonds and glassivation defects should be 
presented in the final report. 

1 . Glassivation shall be examined for delamination, pinholes, and cracks possibly 
induced by the filler in molding compound or mechanical stresses in the package 
(which typically occur at the die comers). 

2. Wire-to-die bonding shall be examined for the following defects: Cratering of the 
bond pad on the die; bond liftoff; wire bonds, which are sheared from the die pads; 
and intermetallic compounds visible more than 0.1 mil beyond the ball attachment 
periphery. 

5.3.9 Die Metallization Examination Using SEM 

One sample or 20% of the lot, whichever is larger, which passed the requirements of 
5.3.5.2 (decapsulation quality) shall be subjected to this test. 

The purpose of this examination is to evaluate acceptability of the die intercoimect 
metallization in accordance with MIL-STD-883, Method 2018 and, in particular, look for 
the following defects: 

• Metallization mechanical defects. 

• Metallization patterning and alignment. 

• Step coverage. 

5.3.9.1 Die-Level Cross-Sectioning. SEM examination and X-ray microanalysis at the 
die-level cross section is performed optionally or when optical examination finds 
suspected defects. The purpose of this test is to evaluate: 

Quality of planarization (if applicable). 

Condition of vias or step coverage. 

Verification of metallization and passivation systems. 

Metallization defects. 

Passivation defects. 



PEM-INST-001 

Section 5. DP A 

Page 29 of 44 



If die cross-sectioning is necessary, the die shall be separated jfrom the plastic package. 
This can be done in two ways: by etching away the paddle, or by removing most of the 
molding compound around the paddle followed by heating the part to a temperature 
above the eutectic or solder melting point. 

Note: It is important to remove all polymer residues from the die before cross-sectioning 
to achieve good quaUty polishing. Acid absorbed in the polymer remnants can mix with 
water during polishing and cause corrosion of metallization. 



PEM-INST-001 

Section 6. Evaluation Analysis 

Page 30 of 44 



6.0 EVALUATION ANALYSIS 



DP A procedures described in Section 5.0 specify minimum requirements for destructive 
physical analysis of PEMs intended for space applications. In some cases additional 
research beyond normal screening or DPA examinations may be necessary. In-depth 
evaluation analysis of the design and materials used in PEMs, custom tailored to analyze 
the technology as applied to the application, may be necessary. A series of tests and 
examinations specially designed by a PEM expert may be undertaken to provide a better 
understanding of part characteristics, materials, and reliability, as necessary. This can 
include additional destructive and non-destructive physical analysis as well as special 
electrical testing, mechanical or environmental stresses, and measurements of the parts. 

The need for an evaluation analysis usually arises due to a part failure in the system-level 
testing, insufficient manufacturer data, and/or general concerns about the reliability of the 
part in specific application conditions. Some examples of these concerns are: effect of 
reflow conditions on mechanical integrity and reliability of the part; probability of ESD or 
EOS failures in the part under certain stress conditions; and effect of special 
environmental (e.g., vacuum) or electrical (e.g., switching transients) conditions on 
reliability, long-term storage at extreme temperatures, effect of the flame retardant used in 
molding compound on long-term wire bond integrity, etc. 

In some cases, to address special quality or reliability concerns, an extended set of 
examinations to characterize design and materials used in PEMs may be required. The 
following list of characteristics gives an example of data that can be required: 

1 . Package-related characterization: Physical dimensions, weight. 

2. Lead-related characterization: Solderability, lead finishing materials (addressing 
tin whiskers problems), mechanical integrity of leads. 

3. Molding compound-related characterization: Outgassing; mechanical 
characteristics (glass transition temperature [Tg], coefficient of thermal expansion 
[CTE]); chemical characteristics (impurities [P, CI, Br, Na]); a-particle emission; 
types of flame retardant; moisture characteristics (moisture diffusion and 
hygroscopic expansion coefficients). 

4. Die-related characterization (materials and design): Passivation, interlayer 
dielectric system, metallization system. 



PEM-INST-001 

Section 7. Derating 

Page 31 of 44 



7.0 DERATING REQUIREMENTS 

Reliability of microcircuits encapsulated in plastics depends significantly on the 
temperature of the part and the level of electrical stress applied during operation. For 
different degradation mechanisms, an increase in operating voltages increases the failure 
rate either according to the power law or the exponential law. However, the most critical 
factor affecting reliability of the parts is the operating temperature, which exponentially 
accelerates most of the failures. Decreasing temperature and electrical stresses during 
operation, or derating the part, significantly decreases the probability of failures. 
Derating can be defined as a method of stress reduction by reducing applied voltages, 
currents, operating fi-equency, and power to increase reliability of the part. 

Derating is widely used for high-reliability military and space-grade applications. It is 
even more essential for commercial PEMs. This is partially due to the fact that the 
thermal resistance for many ceramic or metal packaged parts is much less than for the 
same style of plastic packaged devices. Correspondingly, the operational temperature of 
the die in a plastic package at the same dissipation power level v^dll be higher. 

General derating requirements are listed in Table 4. Taking a conservative approach, 
derating requirements for PEMs should be more stringent than the requirements for their 
high-reliability equivalents. In some cases additional derating may be required based on 
specific application, design, and technology of the part. All part-specific derating shall be 
approved by the project and GSFC Code 562. 

Table 4. Derating Requirements for PEMs 



Stress Parameter 


Derating Equation/Factor 


Digital 


Linear /Mixed Signal 


Maximum Supply Voltage 1/ 


V„+0.5*(V^.,.-V„.,.) 


V,,+0.8*(V™„,-V„,) 


Maximum Input Voltage 


- 


0.8 


Maximum Operating Jimction 
Temperature 12 


0.8 or 95 °C, whichever is 
lesser 


0.7 or 85 °C, whichever is 
lesser 


Maximum Output Current 


0.8 


0.7 


Maximimi Operating Frequency 


0.8 


0.7 



Notes: 

1/ Vnr is the nominal rated power supply voltage; Vmaxr. is the maximum rated power supply voltage. 
2/ For power devices, do not exceed 1 10 °C or 40 °C below the manufacturer's rating, whichever is lower. 



PEM-INST-001 

Section 8. Handling and Storage 

Page 32 of 44 

8.0 HANDLING AND STORAGE REQUIREMENTS 

Scope. This section describes general guidelines for safe handling of PEMs and 
assemblies containing PEMs. There are three major areas of concern that should be taken 
into account when handling and storing PEMs. All are valid up to board-level testing: 

1 . ESP Sensitivity. Most of the PEMs intended for space applications are advanced 
low-voltage, low-power microcircuits, which are extremely sensitive to ESD 
damage. ESD controls to meet NASA-STD-8739 shall be in place. 

2. Delicate Piece Part Packages. Many PEMs have tiny leads, which can be easily 
damaged or contaminated. This can result in poor soldering of the part during 
installation onto boards and cause failure in the event of mechanical stress applied 
to the leads during temperature excursions, mechanical shock, or vibration. 

3. Moisture Absorption and Contamination. Moisture and contamination can 
penetrate through plastic packages and cause degradation and failures during 
testing of the parts, solder reflow process, and operation after integration into the 
system. 

Handling and Storage. Detailed procedures for handling, storing, and maintenance of 
PEMs and assemblies are to be developed. The IPC/JEDEC standard J-STD-033 can be 
used when applicable as a guideline for safe handling and packing of PEMs regarding 
moisture sensitivity. The requirements should follow the entire ground-phase handling 
of the parts including piece part testing, storage prior to installation, and board/system- 
level testing and storage after installation and integration into the system. Below are 
some additional guidelines for measures, which should be undertaken to avoid 
introduction of latent defects during testing, handling, and storing of the flight parts: 

• Reduce handling by reducing the number of screening steps. 

• Avoid contamination of the parts by reducing their exposure to humid 
environments and by using ESD-protective finger cots and ESD-protective bags. 

• Use qualified test labs. Periodically check their conformity to proper handling 
procedures. Ensure that only certified persormel handle flight parts. 

• Taking a conservative approach, all parts with a moisture sensitivity level of less 
than 2 (per IPC/JEDEC J-STD-033) shall be handled as 2a-5a level parts (this 
typically requires a 24 hr bake at 125°C for parts with thickness of -2.5 mm or 
less; and a 48 hr bake at 125°C for parts with thickness ranging from 2.5-4.5 mm). 

• Leads damaged during handling or reformed after forming or damage might 
remain strained and have microcracks. These parts should be marked as such, and 
are not recommended for use. 

Cleaning. Detailed procedures for post installation cleaning and handling of assemblies 
with installed PEMs can be found in IPC SC-60A, "Post Solder Solvent Cleaning 
Handbook." In developing a procedure for safe cleaning of assemblies containing PEMs, 
use IPC-CH-65A, "Guidelines for Cleaning of Printed Boards and Assemblies". 



PEM-INST-001 

Section 9. Manufacturer Information 

Page 33 of 44 

9.0 INFORMATION FROM MANUFACTURERS 

This section describes guidelines for acquiring information from the manufacturer of 
PEMs, which might be useful to assess quality of the parts. 

Table 4 displays questions to be posed and manufacturer data available from Web sites, 
which would help to evaluate the ability of the manufacturer to produce parts with 
consistent quality and to provide acceptable customer support. The data are combined in 
four categories: general information about the part, part design and lifespan assessment, 
manufacturer assessment, and process assessment. 

This information is of mutual interest for the parts engineering community and might be 
usefiil for different GSFC projects. For this reason, the project parts engineer should 
submit a spreadsheet in a standard format according to Table 5 to Code 562 for logging 
into the PEMs database. 

Table 5. Manufacturer Information 



# 


Category 


Information/Question 


1.1 




Part number 


1.2 




Fimction 


1.3 


General Information 


Date code 


1.4 




Package type 


1.5 




Manufacturer 


2.1 




Die process technology 


2.2 




ESD sensitivity level 


2.3 




Moisture sensitivity level 


2.4 


Part 


Date of last die revision 


2.5 




Date of introduction to the market 


2.6 




Expected date for obsolescence 


2.7 




Product storing policy (years to keep in stock) 


2.8 




Packing parts for shipment, moisture control 


2.9 




Type of molding compound and characteristics (glassivation 
temperature, C 1 E, flame retardant) 



Continued on next page. 



PEM-INST-001 

Section 9. Manufacturer Information 

Page 34 of 44 



Table 5 (Continued). Manufacturer Information 



# 


Category 


Information/Question 


3.1 




Vendor facility (location) 


3.2 


Manufacturer 


Point of contact for quality assurance 


3.3 




Quality certification of the vendor (ISO 9000 or equivalent) 


3.4 




Mask revision control 


3.5 




Application support 


3.6 




Part traceability 


4.1 




Availability of Statistical Process Control (SPC) data 


4.2 




What kind of 100% outgoing inspection and screening is used? 


4.3 




Availability of test flowchart 


4.5 


Process 


Availability of reliability and quality assurance handbook 


4.6 




Average outgoing quality (AOQ) 1/ 


4.7 




Major process capability indexes for the part (Cpk) 2/ 


4.8 




Acceptable proportion of failures at high temperature measurements 


4.9 




Radiation hardness of the process or of similar parts 


4.10 




Are there any military parts manufactured using same technology? 



Notes: 

1/ AOQ is the proportion of parts that are outside the manufacturer specification limits. Currently the 
quality assurance system employed by the most established PEMs manufacturers guarantees a minimum 
of a 3-sigma level process. This means that AOQ = 2,700 ppm or 0.27% of all shipped parts might have 
parameters out of the data sheet specification. In some cases this level of failures is below 0.1% and 
even less than two failures in lO' parts for a 6-sigma manufacturer. However, the parts manufactured by 
a 6-sigma process have higher quality only when the parts are used and operate at relatively low 
temperatures. For example, a 6-sigma commercial product, when used in automotive applications, is 
considered a 3-sigma product. 

2/ Cpk is a measure of how well the process fits within the specification limits. It relates process variations 
to the specification limits using a "natural tolerance", 3a, and is applicable only for normal distribution. 
Cpk = [min(HSL - \i), (n - LSL)]/(3ct), where HSL is the higher specification limit, LSL is the lower 
specification limit, n is the mean value, and ct is the standard deviation. Larger Cpk values indicate 
lesser variations in the process and more consistent quality of the product. 



PEM-INST-001 

Appendix A. Policy Basis Discussion 

Page 35 of 44 

10. APPENDIX A. BASIS FOR GSFC POLICY ON THE USE OF 
PLASTIC ENCAPSULATED MICROCIRCUITS (PEMS) 

Prepared by GSFC PEMs Team 

Discussion of Policy Content 

Allowance of the Use of PEMs 

Goddard Space Flight Center (GSFC) is adopting the policy to allow the use of plastic 
encapsulated microcircuits (PEMs) in space flight applications in order to have access to 
the latest technology advances, which are offered in PEMs and only rarely in hermetic 
high-temperature packages. The use of PEMs in space applications can bring advantages 
to the appUcation in terms of performance and part availability, but thorough evaluation 
of the thermal, mechanical, and radiation environment, together with qualification testing 
and screening, are generally required to ensure reliability. 

Environmental Factors 

In space environments, the advantages of PEMs are often accompanied by additional 
risks of failure. This is especially true in applications where PEMs encounter stresses 
(temperature extremes, vacuirai conditions, radiation, etc.) outside the operating 
conditions for which they were designed. PEMs are typically designed to operate within 
two temperature ranges: -40 °C to +85 °C (mdustrial) or °C to +70 °C (commercial) in 
contrast to military hermetic styles, which are generally rated fi-om -55 °C to +125 °C. 
The PEMs manufacturer designs, selects materials, and tests parts to meet the needs of 
their primary customers (conmiercial high volume) and principal end-use envirormients 
(industrial or commercial), not for high-reliability space flight. PEMs are generally 
intended for use in benign environments, where failure in service can be mitigated by 
replacement, maintainability, or repairability. 

The variety of materials and fabrication techniques that may be used in making PEMs 
represents a number of application concerns and reliability risks in space environments. 
Often, these materials and manufacturing techniques have little or no space flight 
heritage. 



pem-inSt-ooi 

Appendix A. Policy Basis Discussion 
Page 36 of 44 



Typical environmental concerns for space flight include: 

• Optical components are at risk of contamination from outgassing of the molding 
material in vacuum environments. 

• Molding materials have varying glass transition temperatures that can affect their 
maximum testing and use temperature. 

• Molding material dimensional creepage with respect to temperature and time may 
place stress on internal bonds and wires. 

• Thermal cycling can generate mechanical stresses on bonds, die paddles, etc. as a 
result of Coefficient of Thermal Expansion (CTE) differences between materials. 

• Molding material in PEMs is usually in contact with the die and may contain ions 
or be the source of secondary emissions that can influence radiation susceptibility 
of the die. These factors can result in PEMs packaged die having lower radiation 
tolerance than the same die hermetically packaged. 

• Operation outside the device's nominal rated temperature range may result in 
rapid deterioration of package properties, weakening of bonds, mechanical 
overstressing of the die, etc. 

• PEMs are all susceptible to moisture ingress and absorption but to varying degrees 
dependent on design, materials, and processing. While not a risk for corrosion or 
other deterioration in space vacuum, moisture can promote corrosion during 
storage and ground level processing as well as "popcoming" during soldering, if 
strict moisture controls are not enacted. 

Other PEMs-Specific Reliability and Application Issues 

High- volume PEMs parts have steadily decreasing time periods between their 
introduction and obsolescence. Various reports put the current time to obsolescence in 
the range of 9 to 1 8 months. Rapid obsolescence has a number of impacts for space flight 
applications. Reprocurement to cover shortfalls or test fallout may not occur before the 
parts are no longer available. Good experience on one project is not usefiil for another 
project with similar needs, if the parts are no longer available. Multiple spacecraft 
programs with builds spaced years apart require a one-time, multi-spacecraft buy or may 
require different parts for successive spacecraft. 

Not only is rapid obsolescence an issue in itself, but it has also led to corresponding 
reduction in designed operational life of the die design. Reports say that PEMs designers 
are now operating on as short as a 5-year life expectancy. Design compromises, such as 
reduced metallization and oxide layer thicknesses, reduce costs but also reliability and life 
expectancy. It has been reported that mask changes can occur as frequently as once a 
month. Die shrink changes are known to have dramatically impacted radiation tolerance. 

PEMs manufacturers generally utilize continuous improvement philosophies that result in 
frequent, unannounced changes to designs, materials, and processes. While improving 



PEM-INST-001 

Appendix A. Policy Basis Discussion 

Page 37 of 44 

performance or cost for the target commercial applications, such changes can have 
unconsidered, negative impacts for space applications. 

For high-reliability products, MIL specifications define the assignment of lot date codes 
and the composition of the corresponding lot. There is no such recognized definition for 
a PEMs lot; it is up to the manufacturer and the needs of their intended market. This 
situation results in traceability and lot sample testing concerns for the space flight user. It 
has been reported that as many as five distinctly different dies of the same fimction have 
been found in a single PEMs lot. In addition, a single lot of PEMs can be processed in a 
number of die fabrication facilities and packaging and test houses throughout the world. 
PEMs of the same nominal device type, but manufactured through different flows in 
different facilities, can be intermixed and marked with the same lot identification. 

Counterfeit parts are an increasing problem in the semiconductor market, particularly 
regarding PEMs. Such parts have an identical or near-identical appearance to genuine 
parts but are known to have substandard quality, reliability, and performance. It is 
essential to evaluate each lot of parts and to vise reputable distributors for PEMs in order 
to reduce the risk of purchasing counterfeit parts. 

Rationale for User-Imposed Qualification Testing and Screening 

PEMs are not governed by strict military standards that require inspection of the die for 
workmanship flaws and the performance of bum-in on each device to remove early 
random failures. In lieu of piece part testing, PEMs vendors typically employ various 
sample-based techniques for calculating reliability. Testing may include proprietary 
testing regimes and employ unique rules governing sample sizes or the exclusion of 
failures fi-om reliability calculations. These variations can make it difficult to compare 
PEM reliability data fi-om vendor to vendor, let alone fi-om PEMs to hermetically sealed 
parts. 

For these reasons, it is not prudent to rely solely on imvalidated reliability data fi-om PEM 
vendors. Screening of PEMs is essential before they are inserted into most flight 
hardware. The most important element in screening for reduced reliability risk for PEMs 
is bum-in. 

Bum-in at the piece part level addresses infant mortality, which represents a significant 
problem for space applications and provides some insight into lot reliability and quality. 
If bum-in at the parts level is not performed, these needs must be addressed by another 
test approach agreed to by the project, such as board-level bum-in, or board/box-level 
environmental stress screening. 

The argument that bum-in of PEMs should be avoided as it reduces the total ionizing 
dose (TDD) resistance of PEMs should be rejected unless solid evidence is produced to 
support the claim. Most studies have shown bum-in to have an impact of 500 Rads or 



PEM-INST-OOl 

Appendix A. Policy Basis Discussion 

Page 38 of 44 

less. To properly evaluate TID of bumed-in parts, the TID test samples must be bumed- 
in prior to testing. 

Radiation lot acceptance testing (RLAT) of PEMs should be performed independently of 
any data that may exist for equivalent or similar hermetically sealed devices, and should 
be performed under the direction of the project radiation specialist. This is necessary as 
market conditions may drive unannounced process changes, creating differences in 
radiation response. It may be possible to dispense with single-event qualification of the 
PEM if data exist for the hermetic device. However, because PEMs are passivated with 
nitride layers, which are known to be responsible for TID sensitivity to pre-irradiatiation 
elevated thermal stresses (PETS), TID characterization should always be independently 
performed. 

Testing and Qualification 

Testing and qualification of EEE parts for space applications are usually performed to 
requirements specific to the risk level desired for the application. Three risk levels are 
currently defined for NASA GSFC Projects. Risk Level One has the lowest inherent 
risk and is intended for critical applications such as single-string, single-point failure and 
mission-essential functions. Risk Level Two has an increased risk and is intended for 
general-purpose spaceflight applications, although use in single-string and single-point 
failure applications may be permissible with project approval. Risk Level Three has an 
unknown risk due to the lack of formalized reliability assessment, screening, and 
qualification, and due to unreported and frequent changes in design, construction and 
materials. These inherent risk levels can be modified by additional testing such that level 
3 parts can be elevated to level 2, and level 2 to level 2+. Upgrading to level 1 is 
theoretically impossible due to lot-specific controls imposed during level 1 manufacturing 
that cannot be imposed once the part has been finished. 

Testing of PEMs should be tailored to the application and based on such factors as 
manufacturer history, analysis of materials, flight history, technology maturity, 
application criticality, and redundancy. 

Basic Screening 

Minimum additional testing for PEMs is established in GSFC EEE-INST-002 for mission 
risk levels 1, 2, and 3. A flow chart of the PEM evaluation process is shown in Figure 5. 

Basic process flow: 

• External visual inspection for workmanship defects such as bubbles or voids in 
the plastic package, separation of the package from the terminations, lead 
corrosion, etc. 



PEM-mST-OOl 

Appendix A. Policy Basis Discussion 

Page 39 of 44 

• Radiography and C-mode Scanning Acoustic Microscopy (C-S AM) to inspect for 
swept bond wires, delaminations, voids, damaged or displaced die, mixed die 
sizes and shapes, etc. 

• Fimctional testing to ensure parts meet requirements over the full application 
range of temperature, power, frequency, voltage, etc. 

• Destructive physical analysis (DPA for PEMs) on samples from each lot to 
inspect for internal workmanship, bond pull, step coverage, die passivation, 
metallization voids, corrosion, contamination, etc. 

• Radiation testing on samples from each lot. Each lot needs to be characterized for 
TID, single event effects (SEE), and displacement damage from charged particles. 

Qualification 

Qualification is required on a lot-by-lot basis unless objective evidence is provided that 
qualification data for a previous lot of the same or similar devices is applicable to the lot 
in question. When qualification testing is required, GSFC EEE-INST-002 defines risk- 
level-specific requirements. 

Typical qualification flows include: 

• Operational life test to simulate performance under application conditions and 
duration; may also be used to estimate life failure rate. 

• Highly accelerated sfress testing (HAST) subjects parts to high levels of 
temperature and humidity to accelerate destructive processes such as corrosion, 
delamination, and die attachment failure detectable by post-HAST DPA. 
Preconditioning of the samples that includes solder exposure is recommended. 

Additional Testing to Lower the Risk of PEMs 

In addition to the basic process flow described previously, the following additional tests 
shall be performed as required by GSFC EEE-INST-002 and as tailored to the PEM for 
its application, based on project requirements: 

• Temperature cycling to excite material CTE mismatches and sfress wirebonds, die 
attachment, etc. 

• HAST or temperature humidity bias to evaluate package integrity. 

• Bum-in for longer duration or at higher sfress levels than the basic requirement. 

• Post-test analysis consisting of PEMs specific DPA. CSAM may also be required. 

Exceptions to Testing 

Reductions to the testing listed in EEE-INST-002 may be permitted with project approval 
on a case-by-case basis, where it can be demonstrated that: 



PEM-INST-001 * 
Appendix A. Policy Basis Discussion 
Page 40 of 44 

• Existing test data for the delivered lot date code demonstrates acceptable results. 

• Use of PEMs represents low risk of functional loss should the part fail. Low risk 
is defined as low application criticality or low potential for loss based on such 
things as light duty cycle, benign environment (minimal temperature extremes, 
radiation exposure, etc.), more than one redundant circuit, short mission life, and 
low mission cost. 

All rationale for such exceptions must be documented. 

Age Control 

Due to molding material creepage, risk of corrosion, material aging, etc., it is necessary to 
limit the age of PEMs to no more than 3 years from date of manufacture to date of 
installation, unless otherwise permitted by the project. Exceptions for age control may be 
granted by the project based on a need for the performance characteristics of older codes, 
or to use PEMs in inventory that is no longer in production. 

Recommended Processing for Storage and Use of PEMs 

• PEMs must be baked out prior to storage and prior to use in order to drive out 
absorbed moisture from the plastic molding material. Storage should be in dry 
environments (Nitrogen purged) at room temperature. 

• The developer shall clean and dry boards using solvents and baking methods that 
will not risk compromising the reliability of parts or boards. 

• The terminations of PEMs should be pretirmed using tin-lead solder to reduce the 
risk of tin whisker growth or to remove gold plating. PEMs typically have pure 
tin-plated terminations, which are a risk for tin whisker growth and subsequent 
system failure due to shorting or plasma arcs. Alternatively, PEMs may be 
available with gold-plated terminations, which are at risk for failure due to gold 
embrittlement. 

• After installation and cleaning, the application of conformal coating to the devices 
is recommended to minimize re-absorption of moisture and to fiirther reduce the 
risk of tin whisker growth. 

Use of Off-the-shelf Assemblies Containing PEMs 

Use and fimction of off-the-shelf units or assemblies that contain PEMs should be 
analyzed for mission criticality. When loss of off-the-shelf units does not compromise 
mission success, on a case-by-case basis, these units may be considered exempt from 
additional PEMs testing requirements, subject to approval by the project. However, 
additional unit-level testing, such as thermal cycling or thermal vacuum testing, may be 
directed by the project in lieu of additional part-level screening. 



PEM-INST-001 

Appendix A. Policy Basis Discussion 

Page 41 of 44 

When failure of such units represents significant compromise to mission success, an 
analysis of the parts used within the units shall be performed. The parts shall be 
evaluated for screening compliance to GSFC EEE-INST-002, and will include a radiation 
analysis. Pending the results of this investigation, units may be required to undergo 
modification for use of higher reliability parts, additional shielding, or replacement with 
radiation-tolerant parts. When no high-reliability parts are available, additional testing of 
the unit may be required. All parts upgrading or additional testing shall be subject to 
project approval. 

If a "high-risk" designation is not acceptable for the application, then additional screening 
must be performed to ensure that the PEMs are consistent with a medium-risk or low-risk 
level as defined in the project MAR and GSFC EEE-INST-002. 

NASA Reference Documents 

Goddard EEE-INST-002 Instructions for EEE Parts Selection, Screening, Qualification, 
and Derating 

Rose, Virmani, and Kadesch (Goddard) Plastic Encapsulated Microcircuit (PEM) 
Guidelines for Screening and Qualification for Space Environments 

S-311-M-70 Specification for Destructive Physical Analysis 

NEPP Document TR04-0600 PEM Derating, Storage, and Qualification Report 

IPC-SC-60A Post-Solder Solvent Cleaning Handbook 



PEM-INST-OOl 

Appendix A. Policy Basis Discussion 

Page 42 of 44 



Start over w/ 
new part or 
adjust 
requirements. 



Initial Design 
PEM or hermetic? 



Is a functionally 

equivalent hermetic 

device available on 

schedule? 



Yes 



No 



Use hermetic 
device w/ 
additional 
testing/screens, 
etc. as needed. 



Is high risk 
acceptable in this 
application? 1/ 



Yes 



No 



Use PEM that 
passes minimal 
screening and any 
additional required 
testing. 



Is upscreened PEM 
acceptable in 
environment and 
application? 



Yes 



PEM must pass 
additional screening to 
establish it as moderate 
or low risk. 2/ 



No 



Can part be repackaged 
hermetically and 
upscreened to low risk? 
Economically? 



Yes 



No 



Use repackaged 
hermetically sealed 
device with any 
additional requhed 
testing (rad, etc.). 



Figure 5. PEM Evaluation Process 



Notes: 



1/ High risk may be acceptable if the impact of part failure on achieving mission goals is minimal. 

2/ Additional screening performed in accordance with GSFC 3 1 1-INST-OOl, or at project direction for 
the appropriate risk level. 



PEM-INST-001 
Appendix B. Product Assurance Methodology 

Page 43 of 44 

11. APPENDIX B. PRODUCT ASSURANCE 
METHODOLOGY 

Background. The product assurance methodology employed by PEM manufacturers is 
sufficient to meet most commercial users' needs. However, this system is significantly 
different compared to military and space-grade parts qualification systems used for 
providing high confidence in parts quality for high-reliability applications. These 
differences in approaches result in uncertainty in the reliability of PEMs, and require the 
end user to perform additional qualification, screening, and analysis of the part to 
compensate for reduced testing by manufacturer. 

General . The classic bathtub curve (see Figure 1, Section 1) consists of three regions: 
infant mortality, usefiil life, and wear-out. The infant mortality failures are induced by 
manufacturing defects and are related to shortcomings in the process control (quality 
failures). The wear-out failures are inherent to the processes used, materials, and design 
of the part. For PEMs, these failures could be due to the die-related and package-related 
limitations. The first group of limitations is similar to the lunitations of high reliability 
parts; e.g., time dependent dielectric breakdown (TDDB), electromigration, hot electron 
effects, and so on. The second group is specific to PEMs and could be due, for example, 
to corrosion of metallization in moisture environments, wire bond or die fi-acture during 
multiple temperature cycling, and other package-related degradation mechanisms. 

The infant mortality period, ti, may last typically for a few months under normal 
operating conditions and is characterized by decreasing failure rate. The usefiil life 
period, tz, lasts normally from 10 to 25+ years and varies significantly depending on the 
device technology, the level of stress during operation, and the wear-out degradation 
process. 

Manufacturers Methodology . Product assurance methodology of most PEM 
manufacturers is based on the philosophy that the reliability must be designed or built 
into the manufacturing process rather than achieved by 100% testing of products. 
According to this methodology the emphasis is on increasing the yield and reducing the 
likelihood of defective parts production by tight process control rather than on detection 
of failures during electrical testing. As a result, for many manufacturers outgoing 
screening of commercial PEMs usually consists of 100% extemal visual inspection, and 
room-temperature fimctional and parametric electrical measurements. High-temperature 
measurements are typically performed on a sample basis and allow a certain level of 
parametric failures. Quality and reUability data provided by most PEM manufacturers are 
mostly estimates based upon the history of performance of a group of parts manufactured 
by similar processes and encapsulated in similar packages. Design and manufactiiring of 
commercial PEMs is mostly driven by a faster time-to-market demand, and the product is 
often released without detailed qualification activities for economical reasons. 



PEM-INST-001- 
Appendix B. Product Assurance Methodology 

Page 44 of 44 

Goddard Space Flight Center. Code 562. Recommended product assurance system for 
PEMs is shown in Figure 2. 



Screening 



Rad. hardness 




Innovative 
screening 



PEM 
handling 



Derating 




Figure 6. GSFC Product Assurance System for PEMs 



Every element of the product assurance system has its limitations, and only a combination 
of all available means can provide cost-effective and comprehensive assessment of the 
quality of the parts and guarantee high reliability for space applications. 

Creating and maintaining a database with the results of PEMs qualification and analysis 
performed for Goddard Space Flight Center (GSFC) projects is an important element in 
the development of the knowledge -based system for quality assurance of PEMs. Reports 
with analysis and summary of the test results, as well as recommendations to improve the 
qualification system, will be released annually by Code 562.